1. Field of the Invention
This invention relates to a totally subcutaneous arterio-venous valved shunt particularly suitable for hemodialysis and a system for coupling a patient to a dialyzing apparatus.
2. Description of the Prior Art
An arterio-venous (AV) shunt is used for providing access to the bloodstream of a patient who requires substantial blood access treatment on a repeated or continuous basis. One of the principal uses of an arterio-venous shunt is in a kidney dialysis operation, wherein a patient's blood must be completely circulated through a dialysis machine as often as twice or three times a week for the entire life of a patient. The purpose of a shunt is to avoid the problems associated with repeated needle cannulation of a patient by providing at least one and preferably two "permanent" outlets from the bloodstream, so that blood can repeatedly be removed from the patient for treatment and then reintroduced into the bloodstream.
The shunt most commonly used for dialysis purposes comprises a pair of elongated tubular segments formed of silicone rubber (Silastic) which are surgically implanted in the arm or the groin of the patient. One tubular segment is connected to a vein and the other tubular segment is connected to an artery. Each tubular segment extends from the blood vessel through a convoluted loop underneath the skin and then protrudes through a continuously open hole in the skin to a fitting that dangles outside the body. The fittings on the outer ends of the tubular segments are constructed so that they may be connected together to provide a closed blood flow loop or separated and attached to a dialysis machine for circulating blood through the dialysis machine. The fittings are connected together to form a closed loop except when the patient is undergoing dialysis. When a patient is to be subjected to dialysis or other such blood treatment, the tubular segments are first clamped to stop the flow of blood, and then the fittings are separated and connected to the dialysis machine. The clamps are then released and blood is permitted to flow through the dialysis machine and back to the body.
Perhaps the most serious drawback with this type of shunt is that infection is a continual problem, both locally and generally. The risk of infection in this type of shunt is caused principally by the fact that the two supracutaneous outlets for connecting the shunt to a dialyzer require the existence of two continuously open holes in the skin. It is extremely difficult to prevent infection from eventually entering the body through these open holes, and the tissue surrounding these open holes is continuously irritated by the constant disturbance and moving of the tubular segments protruding through the holes. Antibiotics are employed to attempt to prevent or control infection, but when infection reaches serious proportions, it becomes necessary to surgically remove the entire shunt from the patient. Since there are only a limited number of acceptable shunt locations in the body, the loss of a shunt location is, in itself, a serious problem, aside from the problems and inconvenience involved in the act of removing one shunt and implanting another in a different location.
Another serious problem with prior art shunts of the nature described above, is that clotting of blood is a dominant risk. The clotting of blood is enhanced by several factors including infection, turbulance within the blood stream, temperature gradients in the blood stream, the stopping of blood flow, and blood flow resistance caused by rough interior tubular surfaces due to the presence of joints or curves in the shunt. When any of these conditions is present, the incidence of blood clotting in any given sampling of people is markedly increased. When a blood clot occurs in either of the tubular segments in the shunt of the prior art, it is frequently difficult or impossible to clear the blockage because of the fact that the tubular shunt follows a convoluted path under the skin, and this path has sharp turns which prevent a catheter from being fitted through the shunt. Thus, when such a shunt clogs, it is frequently necessary to surgically remove the entire shunt and implant a new shunt. This, of course, is undesirable, and the additional surgery and blood vessel work required in the patient increases the likelihood of infection or other harmful side effects.
With the foregoing prior art shunt, the risk of blood clotting is especially significant, because of the multiple curved construction of the shunt necessitated by the subcutaneous and supracutaneous elements and the joints employed in the shunt. The multiple sharp curves and the joints create excessive turbulance, and the supracutaneous portion of the shunt creates fluctuating temperature gradients as the blood flows inside and outside the body through the shunt.
Clotting may also occur with this type of shunt due to misallignment of the subcutaneous tips of the shunt with the blood vessels in which they are mounted. This is a significant problem with this type of shunt, because the anchorage of the shunt in the body is sustained primarily by the punctures through the skin which hold the shunt in position. Movement of clothing or other disturbance of the portion of the shunt that extends outside the body causes a continual disturbance to the shunt itself, and this disturbance is translated to the connections between the tips of the shunt and the blood vessels to which they are attached. Movement of the tips is also encouraged during the beginning and ending phases of the dialysis function, when manipulation of the external portions of the shunt is necessary.
Another reason why the foregoing prior art shunt enhances blood clotting is that the blood stream is completely stopped at the beginning and ending phases of dialysis, when it is necessary to clamp the tubular segments in order to connect and disconnect the fittings from the dialysis machine. This stoppage of blood flow greatly increases the prospects of blood clotting.
The problem with blood clotting is especially significant in home kidney dialysis operations, where a kidney dialysis patient performs the dialysis by himself at home. When a blood clot occurs in a patient's shunt, he has no recourse but to abandon the home treatment procedure and seek immediate corrective measures from his doctor.
Another disadvantage with a shunt of this nature is that the exposed outer connections make it possible for the shunt to become completely dislodged accidentally, and patients are required to limIt movement for fear of causing an accidental dislodging or misalignment of the shunt. Further, continuous care is involved in a never ending attempt to keep the shunt clean and, as far as possible, free from infection. Still another drawback with a shunt of this nature is that the mere existence of the tubular loop dangling outsIde the body through open holes in the skin is cosmetically, as well as hygenically, undesirable.
Another type of shunt that has been developed comprises a U-shaped loop, one end of which is connected to a vein and the other end of which is connected to an artery. The loop itself may be mounted in the body subcutaneously, but outlet conduits extending from the sides of the loop protrude through open holes in the skin to outlet terminals on the outside of the body. Removable plugs fit in the outlet tubes and block the flow through these tubes during normal conditions. To subject a person to dialysis, the plugs are removed and the outlet terminals are connected to inlet fittings for a dialysis machine.
This type of shunt avoids certain of the problems with the other prior art shunt discussed above, namely, the shunt is substantially shorter and does not have the multiple curves of the prior shunt. However, several of the deficiencies of the other shunt are present in this shunt as well. One of the principal deficiencies is that this shunt still has outlets on the outside of the skin, and continuously open holes are still required in the skin to permit the shunts to extend through the skin. Thus, the most serious problem, infection, is still present. The likelihood of blood clotting in the outlet conduits in this type of shunt is substantial because the outlet conduits have to be clamped closed (causing blood stagnation at the beginning and end of dialysis). Further, any shunt having external outlets is subject to the problems of misaligning with the blood vessels in which it is mounted.
One of the principal objects of the present invention is to provide an arterio-venous shunt which is disposed completely below the surface of the skin of the patient so as to eliminate the problems of infection, clotting, and accidental dislodging of the shunt.
Another object of the present invention is to provide an arterio-venous shunt in a small and compact form, which is easy to install in a single piece in the limb of the patient.
Another object of the present invention is to provide an arterio-venous shunt which is positively self-stabilizing beneath the skin.
Still another object of the present invention is to provide an arterio-venous shunt that minimizes the incidence of blood clotting by (a) reducing blood flow turbulence; (b) reducing stagnation pockets in the shunt; (c) reducing blood flow resistance by reducing the total length of the shunt; and (d) eliminating temperature gradients in the blood flow.
It is the further object of the present invention to provide an arterio-venous shunt that can easily be declotted and cleaned by a conventional Fogarty catheter, in the event that clotting should ever occur in the shunt.